THE EFFECT UPON THE FATTY ACID COMPOSITION OF MILK OF FEEDING TROPICAL PASTURES TO JERSEY COWS

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1 Proc. Aust. Soc. Anim. Prod. (1972) 9: 297 THE EFFECT UPON THE FATTY ACID COMPOSITION OF MILK OF FEEDING TROPICAL PASTURES TO JERSEY COWS T. H. STOBBS* and D. J. BRETT** Summary The fatty acid composition of milkfat from Jersey cows grazing tropical pastures was determined by gas chromatography. The relative proportions of fatty acids were compared in milk produced when cows grazed nitrogen fertilised Digitaria decumbens, nitrogen fertilised Setaria sphacelata and Setaria sphacelata/ Phaseolus atropurpureus (setaria/sirato) pasture in a 3 x 3 (5) latin square, or received additional concentrate supplements. The proportion of short chain fatty acids (GG6) decreased and the proportion of long chain acids, particularly oleic acid, increased when milk yield was reduced by grazing the three tropical pastures. Milk production was highest when COWS were supplemented with concentrates and lowest on the setaria/siratro feed. Results suggest that fatty acid analyses could be used to rank tropical pastures for milk production, and to compare grazing management methods for these pastures. I. INTRODUCTION The lactating dairy cow augments or conserves dietary nutrients by removing or storing body fat. For example, a high producing cow in the first month or two of lactation is usually in negative energy balance even when offered liberal amounts of an adequate diet, and draws upon body reserves to maintain milk production. Numerous : tudies have shown that short chain fatty acids in milk are synthesised in the mammary gland from acetate and to a lesser extent from p- hydroxybutyrate (Linzell 1968), while the long chain acids are extracted by the gland mainly from triglycerides of chylomicrons and low-density lipoproteins ( Lascelles et CZZ. 1964; Jones 1969). Milkfat from COWS receiving a sub-optimum plane of nutrition and drawing upon body reserves has been shown to contain a high proportion of oleic acid and a low proportion of (C&16) fatty acids (Mayhead and Barnicoat 1956; Luick and Smith 1963; Munford et az. 1964; Parodi 1970). WSIRO, Division of Tropical Pastures, Cunningham Laboratory, St. Lucia, Brisbane, 4067, **CSIRO, Division of,4nimal Physiology, Cunningham Laboratory, St. Lucia, Brisbane, 4067.

2 Grazing experiments (Stobbs 197 la) and pen-feeding trials (Minson 197 1) have shown that tropical pasture species generally have lower nutritive quality than temperate species, and that considerable variability in quality exists. A study was therefore initiated at the CSIRO, Pasture Research Station, Samford, to investigate the effect upon milk production and milk fatty acid composition of feeding three tropical pastures and a grass/concentrate mixture to lactating cows. II. MATERIALS AND METHODS (a) Pastures Six 0.21 ha replicates of Digitaria decumbens (pangola), Setaria sphacelata cv. Kazungula (setaria) and Setaria sphacelata cv. Kazungula/phmeolus atropurpureus cv. Siratro (setaria/siratro) were established in a randomised block design in October 19609, and received 400 kg/ha of single superphosphate at establishment and in September 1970, before the grazing trial commenced. Nitrogen (50 kg/ha) was applied monthly to the pangola and setaria pastures except in June, July and August. Siratro made up only 5 per cent of the dry matter in the setaria/siratro swards because this legume grew slowly in spring by comparison with setaria. (b) Animals and management Fifteen Jersey cows, calved on a high plane of nutrition, were allotted to three treatment groups 5-8 weeks after calving according to stage of lactation, milk yield and Iiveweight. The groups of five cows grazed the pasture types according to a 3 x 3 extra period latin square design. For 14 days prior to and 14 days following the experiment, all cows communally grazed on Chloris gayana cv. Pioneer Rhodes pasture, supplemented with 3 kg/head/day of a balanced concentrate supplement which was based on sorghum and cotton seed meal. The experimental periods, during which no supplements were fed, were of 14 days duration. Four days were allowed for standardisation followed by two 5-day measurement periods (M.P.). Replicates were rotationally grazed using extra non-experimental cows where necessary to allow a minimum of 1000 kg/ha (actual mean 1500 kg/ha) dry green material of 2-3 weeks herbage regrowth to be constantly available. The cows were milked twice daily, and spent about 4h/day away from pastures. Water and shade were constantly available. (c) Pasture and milk sampling The yield of dried green herbage (total dry matter excluding dead material) before and after grazing was estimated in each second measurement period using an electronic capacitance meter (Jones and Haydock 1970). Milk yields of individual cows were recorded and 2 per cent aliquots, taken at each milking, were bulked for each measurement period (M.& and M.P.2) and also for seven 2-day periods in the first experimental period. These samples were analysed for butter fat, solids-not-fat, protein and casein (Stobbs 1971b). 298

3 (d) Fatty acid analyses Fat was extracted by TeSa reagent, methylated according to Christopherson and Glass ( 1969), and the methyl esters separated on a Shimadzu GC-1C gas chromatograph using a m x 3 mm diethylene glycol succinate column ( 17 per cent DEGS, mesh chromosorb W. acid washed) which was matrix temperature programmed from C. The proportion of fatty acids in milkfat were expressed as molar percentages. III. RESULTS Mean daily milk production fell (P > 0.01) from 15.2 kg/cow during the preliminary period to a mean of 11.5 kg/cow during the last five days of the first experimental period. At this time there was no significant difference between treatments (P > 0.05). However, over all the experimental periods of the latin square, pangola and setaria produced significantly (P < 0.05) more milk than the setaria/siratro pastures, milk yields averaging 9.7, 9.3 and 8.5 kg/cow/day respectively. Milk from cows grazing the setaria/siratro pasture had a higher butter fat content (P < 0.05) and a lower solids-not-fat content (P < O.OS), particularly protein (P < 0.05) and casein (P < 0.05) than milk produced from cows grazing the pangola and setaria pastures. The residual effect of previous treatments upon milk production was non-significant. The molar percentage of short chain fatty acids, particularly Cg, Cg, CIOr Cl2 an1 Cl4 was significantly lower, and conversely the molar percentage of long chain fatty acids, especially Cis 1 was significantly higher when cows changed from supplemented tropical pasture to unsupplemented tropical pastures. When the cows returned to supplemented tropical pasture in the final period, the milk fatty acid composition returned to the original proportions. During the three periods of the latin square, the oleic acid (C,,. *) content of milk produced on setaria/siratro pasture was higher than that of milkfat produced on the pangola (P < 0.01) or setaria (P < 0.05) treatments (Table 1). Within each treatment period the oleic acid content of milkfat in the first measurement period (M.P.,) was higher (P < 0.01) than in the second measurement period (M.P.2). A TABLE 1 Mean proportiun of oleic acid (molar percentage) in milkfat in each of the sampling periods 299

4 negative correlation r = (P < 0.001) was found to exist between mean oleic acid proportion and daily milk production. Over the first 14 day experimental period, when samples were also taken at 2 day intervals, there was a significant linear decline in the content of CG, Cg, ClO, CIZ and Cl4 fatty acids. Pooled totals for these fatty acids together with an estimate of standard deviation of a single determination are shown in Figure 1. A significant quadratic, as well as a significant linear decrease in the content of short chain fatty acids with time was measured. Milk produced on the setaria/siratro treatment had a lower proportion (P < 0.05) of short chain fatty acids than milk produced on the other two treatments. Conversely, the proportion of oleic acid in the milkfat increased, and after only 6 days, milk from setaria/siratro pasture had a higher (P < 0.05) oleic acid content than milk from the other two treatments. IV. DISCUSSION The type of feed consumed affected milk production and also the fatty acid composition of the milkfat. Milkfat produced when cows grazed the three tropical pastures, particularly setaria/siratro, contained a lower proportion of short chain fatty acids than when supplementary concentrates were provided; this was most probably due to a lower quantity of short chain milk fatty acids being synthesised when animals received a sub-optimum plane of nutrition. The consequent higher 300

5 proportion of oleic acid in the milk when cows grazed unsupplemented tropical pastures was in part a reflection of the mobilisation of body reserves as the cows attempted to sustain milk production. The quantity of food consumed by cows can markedly affect the fatty acid composition of milk. Luick and Smith (1963) showed that both fasting and starving due to acute ketosis reduce the proportion of short chain fatty acids, with a compensatory increase in the long chain fatty acids, especially oleic acid. In the current work, a mean of 1500 kg/ha of dried green material was offered in an attempt to,ensure that differences in milk production were due to the quality of the herbage being grazed rather than feed availability (Ivins, Dilnot and Davison 1958). Pen feeding studies (Stobbs and Brett, unpublished data) have shown a reduction in short chain fatty acids and an increase in long chain fatty acids in milkfat when the intake of digestible nutrients was reduced. The fatty acid composition of milkfat has been found to vary with stage of lactation (Decaen and Adda 1966; Saito and Nakawishi 1970). Stull elt ae. ( 1966) have shown with cows fed uniform diets that the proportion of Cl8 acids decreases while the C6-C14 acids increase with stage of lactation; the most marked changes occur during the first 6-8 weeks after calving when intake is increasing (Hutton 1963). However McDowall ( 1962) has shown that seasonal changes in nutrition have a greater influence upon fat composition of milk than stage of lactation. In the present experiment individual cow variability was not investigated; but variability between balanced groups of 5 cows was low, since the fatty acid content of milk from uniform diets in the preliminary and final periods was similar for each of the groups (see Table 1 and Figure 1). The results suggest that fatty acid analyses of milkfat could probably be used in short-term grazing trials as a means of ranking feeds in terms of their milk producing ability. The lower potential of setaria/siratro pasture compared with the nitrogen fertilised grass pastures was identified after only six days by a lower proportion of short-chain fatty acids and a higher proportion of oleic acid in milkfat, whereas there were no significant differences in milk production between these treatments at this stage. Milk production reflects the intake of nutrients supplied by the feed, augmented if necessary from body reserves, and in shortterm trials may not indicate the true value of a feed. This work suggests that the use of body fat to sustain milk production can be determined from fatty acid analyses. If this is confirmed in later work, the technique will be extremely valuable for comparing different pastures and grazing management treatments, particularly in short term studies. V. REFERENCES Christopherson, S. W. and Glass, R. L. (1969). J ournal of Dairy Science, 52: Decaen, C. and Adda, J. (1966). Proceedings of the Seventeenth Internatiortul Dairy Congress, A: 161. Hutton, J. B. (1963). Proceedings of the New Zealand Society of Animal Production, 23: 39. Tvins, J. D., Dilnot, J., and Davison, J. (1958). Journal of the British Grassland Society, 13: 23. Jones, E. A. (1969). Journal of Dairy Research, 36:

6 Jones, R. J., and Haydock, K. P. (1970). Journal of Agricultural Science, Cambridge, 75: 27. Lascelles, A. K., Hardwick, D. C., Linzell, J. L. and Mephan, J. ( 1964). Biochemistry Journal, 92: 36. Linzell, J. L. (1968). Proceedings of the Nutrition Society, 27: 44. Luick. J. R. and Smith, L. M. (1963). Journal of Dairy Science, 46: McDowall, (1962). Journal of Dairy Research, 29: 307. Mayhead, J. W., and Bamicoat, C. R. (1956). Journal of Dairy Research, 23: 238. Minson, D. J. (1971). Journal of the Australian Institute of Agriculturd Scienice (in pre). Munford, R. E., Campbell, I. L., McDowall, F. H., and Davey, A. W. F. ( 1964). Journal of Dairy Research, 31: 59. Parodi, P. W. (1970). Australian Journal of Dairy Technology, 25: 200. Saito, T. and Nakawishi, I. T. ( 1970). Japanese Journal of Dairy Science, 19: 100. Stobbs, T. H. (1971a).. Tropical Grasslands 5: 159. Stobbs, T. H. (1971b). Australian Journal of experimental Agriculture and Animal HUSbandry, 11: 268. Stull, J. W., Brown, W. H., Valdez, C., and Tucker, H. (1966). Journal of Dairy Science, 49: